The hot water system in many homes, offices and other facilities includes a hot water heater that receives cold water from a water source, heats the water and delivers the heated water through pipes to a location where heated water is needed. The hot water heater is often located on a lower level of such facilities near where potable water is received. Kitchens and bathrooms are generally located on upper levels and may be remote from the hot water heater.
A hot water faucet is opened to obtain hot water from a hot water heater. Unless hot water was obtained from the faucet a short time earlier, water must run from the faucet for a sufficient time to remove all the cold water from the pipe between the faucet and the hot water heater plus heating the pipe. The cold water discharged from the hot water faucet passes into a drain pipe and to a sewer system. The quantity of water that is lost can be significant. Insulation on the pipe can keep hot water in the pipe and the pipe at least warm for some period of time. However, insulation will not keep the water and pipe hot for an extended period of time.
Potable water is generally pumped from a water source by pumps. The pumps also maintain pressure in a water system or elevate water to a storage tower. The water is generally filtered and treated with some chemicals to insure that water born organisms do not make people sick. In a few areas, salt water is evaporated and then condensed to provide potable water. This pumping, filtering and chemical treatment of water is expensive. The heat required to distill salt water is also expensive. Sanitary sewer systems, where available, are constructed and operated by fees added to water bills thereby further increasing the cost of water.
Instant or nearly instant hot water may be obtained by adding a flow through heater to the hot water pipe near the hot water faucet. These electric heaters work well to heat a relative small quantity of water for making a hot drink or some food products. Such heaters have relatively low capacity. The purchase, installation and operation of an instant or nearly instant hot water heater is expensive. However, such heaters may reduce water usage. Such reduction of water usage is probably more significant than most home owners believe. However installation and operating costs of a flow through heater are significant and may exceed the cost savings due to water use reduction.
Instant or nearly instant hot water may also be provided by a pump or pumps that circulate water through a hot water supply pipe and back to the hot water heater. Such pumps run constantly and require a significant amount of electricity. These water circulating systems are generally reliable. The water that is returned to the water heater has cooled somewhat in the hot water supply line. The return flow of water by the pump is through a cold water supply pipe in some pump systems. After the pump runs for a period of time, there is hot water in a portion of the cold water supply pipe. Opening a cold water faucet will in some cases result in the discharge of hot water. Hot water in the cold drinking water is undesirable. Some chemicals employed to treat potable water will become gases at an elevated temperature and atmospheric pressure. The gases will separate from the water. The separated gases may be harmful to people and animals. Although the need for hot water may only occur a few times each day, the pump circulates water continuously.
Pumps employed to return cooled hot water to a hot water heater produce pressure changes in a pipe system that may result in vibrations and noise. Noise generated by a pump resonates throughout the plumbing system and often is objectionable. Although the need for hot water may only occur a few times each day, the pump cycles, as required, 24 hours per day.
A recent innovation used to provide hot water is the high flow, point of use water heaters that can be placed adjacent to areas such as showers and laundries that require a large quantity of hot water in a very limited time. They produce hot water almost instantly by the rapid infusion of large quantities of energy. They work well, and reduce the amount of cooled hot water discharges to the drain. Often they are secondary serving only a portion of the building, the main source being a standard hot water heater. The purchase price may be two to three times the cost of a standard hot water heater. Infrastructure is expensive due to the required capacity of 180,000 B.T.U.s of energy at an instant as need basis. If the high capacity point of use heater is selected, there is additional cost to provide venting of exhaust gas, and a larger gas meter to provide that fuel.
To overcome the delay in obtaining hot water, people often increase the thermostatic control on the hot water heater to the maximum or near maximum setting, thereby increasing the output temperature of water from a relatively safe one hundred and thirty degrees (130°) Fahrenheit to a potentially scalding temperature of one hundred and sixty degrees (160°). Skin exposure to 160° water can result in serious scalding in as little as one second. New regulations in some areas limit delivered water temperature through a faucet to 110 degrees Fahrenheit. The majority of grandfathered faucets in use today do not provide this protection, predictably resulting in many serious injuries. It will be years before all of the grandfathered faucets are replaced to prevent delivery of hot water above a regulation temperature.